It is hard to figure out exactly what you are trying to do from the question. I'll take a guess and say that you want to add an extra compile task in addition to those provided out of the box by the java plugin.
The easiest way to do this is probably to specify a new sourceSet
called 'speedTest'. This will generate a configuration
called 'speedTest' which you can use to specify your dependencies within a dependencies
block. It will also generate a task called compileSpeedTestJava
for you.
For an example, take a look at defining new source sets in the Java plugin documentation
In general it seems that you have some incorrect assumptions about how dependency management works with Gradle. I would echo the advice of the others to read the 'Dependency Management' chapters of the user guide again :)